IMO this is also related to https://bugs.chromium.org/p/chromium/issues/detail?id=761763

#1, the OS choice is in the title bar so that users know which platform they're currently viewing details for, not just as a means for toggling it.

#2, The OS choice made via dropdown persists across the full dashboard and has impact on other pages, not just the "First Release" column - it changes the detailed "Commit" page, "Milestones" and "Releases" pages as well.  Given that most developers or users are going to want to use different pages in conjunction, having OS selection in shared UI (the toolbar) is the best solution we could think of.  We'd played around with placing this in a "Settings" dialog, but most users would miss that and then not have any idea how to change OS, so that was definitely worse.  Embedding the choice in the pages that utilize it would likely mean having it in different locations on each page, which also doesn't feel natural.

So, perhaps it's not perfect, but it's the best implementation I can think of - if you have concrete suggestions I'm happy to hear them, but otherwise I think this is a WontFix.

Cleaning up title a bit to match other feature requests and bumping priority.  See also https://bugs.chromium.org/p/chromium/issues/detail?id=763557#c3 for thoughts on refactoring the design a bit; this would imply we'd move platform selection into the page itself, which could help make things more intuitive.

Ben, looks like doing some work on this, assigning this to you now. please un-assign yourself if that is not the case.

No longer on the Chrome team, e-mail me @google.com if any attention still required from me here, otherwise good luck!